Recombinant protein truncation strategy for inducing bactericidal antibodies to the macrophage infectivity potentiator protein of Neisseria meningitidis and circumventing potential cross-reactivity with human FK506-binding proteins

A recombinant (r) Macrophage Infectivity Potentiator (MIP) protein of Neisseria meningitidis induces significant serum bactericidal antibody production in mice and is a candidate meningococcal vaccine antigen. However, bioinformatics analysis of MIP showed some amino acid sequence similarity with human FK506-binding proteins (FKBPs) in residues 166-252 located in the globular domain of the protein. To circumvent the potential concern over generating antibodies that could recognise human proteins, we immunised mice with recombinant Truncated Type I rMIP proteins that lacked the globular domain and the signal leader peptide (LP) signal sequence (amino acids 1-22) and contained the HIS purification tag at either the N- or C-terminus. The immunogenicity of Truncated rMIP proteins was compared to Full rMIP proteins (containing the globular domain) with either a N- or C-terminal HIS tag and with or without the LP sequence. By comparing the functional murine antibody responses to these various constructs, we identified that C-term HIS Truncated rMIP (-LP) delivered in liposomes induced high levels of antibodies that bound to the surface of wild-type but not ?mip mutant meningococci and showed bactericidal activity against homologous Type I MIP (median titres of 128-256) and heterologous Type II and III (median titres of 256-512) strains, thereby providing at least 82% serogroup B strain coverage. In contrast, in constructs lacking the LP, placement of the HIS tag at the N-terminus appeared to abrogate bactericidal activity. The strategy used in this study would obviate any potential concerns regarding the use of MIP antigens for inclusion in bacterial vaccines